The present invention relates to a flat electron addressed device including apparatus for scanning electron beams over a target element thereof, and particularly to a structure for confining and guiding the beams and for selectively deflecting the beams toward the target.
There are various devices, such as optical display devices, information storage devices, scan converters, optical pick-up devices and the like, which include a target over which a beam of electrons is scanned to address the device. In an optical display device, such as a picture tube, the target is a phosphor screen. In an information storage device, the target may be a semiconductor storage element. In a scan converter and an optical pick-up device the target may be a photoconductor.
The electron beam addressed device of the present invention may be any device having a target over which a beam of electrons is scanned to address the target. For example, the device may be an information or storage device having a target of the type shown in U.S. Pat. No. 3,675,134 to E. Luedicke et al., issued July 4, 1972 entitled "Method of Operating an Information Storage Tube", or a scan converter having a target of the type shown in U.S. Pat. No. 3,182,223 to J. T. McNaney, issued May 4, 1965 entitled "Data Storage System With Light Beam Write/Readout", or an optical pick-up device having a target of the type shown in U.S. Pat. No. 2,967,254 to S. V. Forgue, issued Jan. 3, 1961 entitled "Composite Photoconductive Layer" or an optical display device having a target of the type shown in U.S. Pat. No. 2,928,014 to W. R. Aiken et al., issued Mar. 8, 1960 entitled "Electronic Device Cathode Ray Tube". A preferred device is an optical display device and the present invention will be described in detail as embodied in an optical display device. However, the other types of electron beam addressed devices can be constructed similarly to the optical display device by substituting the particular target of the electron beam addressed device for the phosphor screen target of the optical display device.
It has long been a desire to reduce the depth dimension of such electron beam addressed devices, particularly picture tubes, to provide a substantially flat device. With regard to optical display devices, one structure which has been proposed includes a thin box-like envelope with one of the large sides thereof constituting a faceplate on which a phosphor screen is disposed. An electron gun directs electrons across the tube in a path substantially parallel to the screen. Deflection elements are provided to selectively deflect the electrons onto successive points of the screen to achieve the desired scanning thereof. A tube of this type is shown in U.S. Pat. No. 2,928,014 to W. R. Aiken et al., issued Mar. 8, 1960 entitled "Electronic Device Cathode Ray Tubes".
In using this technique a problem has arisen in making flat display devices having large area screens, such as screens which are about 75 centimeters by 100 centimeters. For such large size devices some type of internal support structure is required to prevent the evacuated envelope from collapsing. A device having such internal support is shown in U.S. Pat. No. 2,858,464 to W. L. Roberts, issued Oct. 28, 1958 entitled "Cathode Ray Tube". In a tube having internal support structure, the confinement and guiding of the electron beam is more critical to prevent the supporting structure from interfering with the electron beam.
As a beam of electrons moves away from its source, the electrons tend to spread out, making the size of the beam larger in cross-section. If the electrons spread out enough so that a substantial amount of them contact the supporting structure, parts of the tube become charged and cause malfunctioning of the tube.